In the United States, stroke-related illness is the leading cause of long-term disability. Each year approximately 750,000 individuals in this country suffer a stroke, and for those who survive, a majority will be afflicted with a motor disability. There are currently 4.5 million U.S. citizens permanently disabled by stroke, with annual health-care costs of approximately $50 billion.
Neuromuscular symptoms of stroke include, but are not limited to, muscular paresis (i.e., reduced ability to activate muscles), plegia (i.e., complete paralysis of muscles), and dyssynergia (i.e., inability to activate certain muscles without inadvertent activation of inappropriate muscles in the same limb or other limbs). Often a stroke patient will be plegic at a joint for attempted movement in one direction and paretic in the other direction.
The diagnosis of plegia in stroke victims does not necessarily mean that the individual is completely incapable of activating the appropriate muscles at a joint. Rather, in many cases, the absence of movement is a result of insufficient levels of muscle activation and joint torque to achieve overt movement. Moreover, movement at a joint may be prevented by inadvertent, concomitant activation of the muscles on the wrong side of the joint (i.e., dyssynergia), whereby inadvertent activation overpowers weak activation of muscles on the appropriate side of the joint.
In certain embodiments of AMES therapy described in U.S. Pat. No. 6,878,122, which is assigned to the assignee of this patent application, patients with neuromuscular disorders receive feedback in the form of joint torque. The patients are fed back the amount of torque they are able to produce voluntarily while assisting joint motion produced by a motorized robotic device. If the patient is incapable of producing joint torque during AMES treatment, the patient receives no feedback, even if the patient's attempts to assist movement produce appropriate, but weak, activation of the appropriate muscles. Without useful feedback, these weak, but not completely paralyzed, patients are less likely to benefit from treatment.